@keyframes run{
    /* 0%可以用from表示 */
    0%{
        width:100px;
        height: 100px;
        background-color: orange;
    }
    25%{
        width:200px;
        height: 200px;
        background-color: aquamarine;
    }
    50%{
        width:100px;
        height: 100px;
        background-color: pink;
    }
    /* 100%可以用from表示 */
    100%{
        width:50px;
        height: 50px;
        background-color: orange;
    }
}

div{
    width:100px;
    height: 100px;
    background-color: orange;
    animation: run 4s;
}

div:hover{
    width:200px;
    height: 300px;
    background-color: aquamarine;
}